This invention relates generally to microprocessor controlled systems and in particular to systems for detecting faults in the microprocessor and in the machine which the microprocessor controls.
In recent years, many industrial and consumer machines have included a microprocessor to control machine operation. As a result, machine operation has been made more accurate and sometimes more complicated. In addition, microprocessors have become larger and more complex in order to meet the demand for more sophisticated machine control.
As a result of the increased complexity of microprocessors, it has become more difficult to isolate defects in both the microprocessor and the machine which is controlled thereby. In some instances, a defect which appears to be a malfunction of the machine may actually be a microprocessor malfunction. Conversely, an apparent microprocessor malfunction may actually be a malfunction of the machine.
Because of the uncertainty as to where a defect resides, it has been customary to physically remove the microprocessor in order to check the operation of the machine independently of the operation of the microprocessor. However, manual handling of the microprocessor may result in further damage to it, particularly to its input/output leads.
Another proposed solution to finding machine malfunctions is to incorporate a special program in the microprocessor by which the various functions of the machine are exercised. The drawback to this solution is that: (1) if the machine operates improperly under the special program, it may be either a microprocessor malfunction or a machine malfunction which is responsible; (2) the special test programs are usually incomplete or inadequate to completely test the machine, because it is impractical to have a test program for every possible machine failure; and (3) prior special test programs take up too much room in the microprocessor's memory. Hence, the prior solutions to isolating machine and/or microprocessor faults may lead to uncertainties and involve prolonged testing.